The invention is directed towards semiconductor packaging and more specifically, towards determining the hermeticity of semiconductor packaging.
Many semiconductor devices are sensitive to contamination, humidity, and other environmental factors. A package for such a device must be hermetically sealed to protect it from harm. The package is subsequently checked for leaks to ensure that it is properly sealed.
One existing method for detecting a leaky package is to place it in an environment pressurized with helium gas. If the package has a leak, helium will be pushed into the package cavity. Next, the package is removed to a chamber that is connected to a mass spectrometer. The chamber is vacuum-pumped, so any helium that found its way into the package cavity will be suctioned out. If the mass spectrometer detects helium, the package was not properly sealed. This method and others are described in more detail in the Joint Electron Device Engineering Council (JEDEC) standard for hermeticity, JESD22-A109-A, published July 2001.
The prior aft methods have a few drawbacks, however. After a leaky package is flooded with gas, some of the trapped gas inevitably leaks back out when the package is moved to the vacuum chamber. The package cavity must be large enough to allow for this leakage and still retain enough helium to be detected by the mass spectrometer. Additionally, only a single package can be tested at a time using the prior methods. When multiple packages are placed into the vacuum chamber, the prior methods cannot pinpoint which of the packages has a leak.
Current packaging processes have evolved to create much smaller package cavities than before. Wafer-level packaging is one such process. In wafer-level packaging, the semiconductor device is packaged while it remains on the wafer. The device is capped with a cap wafer, thus sandwiching the device between the two wafers and forming a package. Thousands of devices on a wafer can be packaged simultaneously in this fashion. Later, the devices are sawed apart or otherwise separated from each other.
These wafer-level packages are too small to be tested for hermeticity using the prior art methods. The amount of gas trapped within the wafer-level packages is so small that, after accounting for gas leakage, not enough gas remains behind in the package to obtain an accurate measurement. Furthermore, since the prior art methods can only test one package separately at a time, testing the thousands of wafer-level packages created per wafer would be a very time-consuming and expensive process.
In a preferred embodiment of the present invention, a method for determining the hermeticity of a semiconductor package is disclosed. This embodiment will hereinafter be referred to as the encapsulation method. First, the device is packaged in a chamber flooded with gas, trapping gas within the package cavity. Next, the package is subjected to a vacuum. If the package has a leak, the previously trapped gas will be sucked out. However, a properly sealed package will not be affected by the vacuum suction, and the gas will remain inside. Finally, the package is scanned using a spectrometer. If the spectrometer does not detect any gas, the package has a leak. If the spectrometer detects gas within the package cavity, then the package is hermetically sealed.
An alternate method for determining the hermeticity of a semiconductor device package is also disclosed. This method will hereinafter be referred to as the infiltration method. First, the device is packaged. Next, the package is immersed in a pressurized liquid. If the package has a leak, the pressure on the liquid will force liquid into the package cavity. However, the cavity of a properly sealed package will remain empty and dry. Finally, the package is scanned using a spectrometer. If the spectrometer detects liquid within the package, the package has a leak. If the spectrometer does not detect any liquid, then the package was properly sealed.
These methods can be successfully used on packages too small to be reliably tested before Furthermore, the packages do not have to be separated from each other before their hermeticity can be testedxe2x80x94the packages can remain on the wafer during hermeticity testing.
Further features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying exemplary drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.